Aluminum alloy resistance spot weldingAluminum alloy resistance spot welding
(1) features of resistance spot welding of aluminum alloy
Aluminum alloy resistance spot welding process is under the pressure of the electrode, by the resistance of hot melting aluminum, the process of connecting together. Due to the low melting point of aluminum alloy, high linear expansion rate, high conductivity, surface oxidation and other characteristics, aluminum spot welding must use large current, short time, multi-pulse, large electrode pressure, so aluminum spot welding output large current to the welding machine, transformer and welding gun power supply requirements, large current easy to produce strong magnetic field, welding tooling needs anti-magnetic; The large electrode pressure requires a strong and reliable welding gun structure, and equipped with special electrode head to solve the problem of aluminum alloy surface oxide layer. At present, the resistance spot welding methods of aluminum alloy mainly include the American application of WTCTip Dressing (aluminum spot welding with spiral electrode cap) and the German application of Deltaspot (aluminum spot welding with electrode belt).
(2) application of American aluminum spot welding -- WTC Tip Dressing
Tip Dressing end parameter correction technology is adopted in WTC aluminum spot welding equipment in the United States, and GM patented aluminum spot welding electrode cap is utilized. The surface of this electrode head has a special ring pattern, as shown in FIG. 2, which can generate different stress zones on the aluminum surface. The oxidation film can be broken to obtain a controllable contact resistance. When using this special ring pattern electrode cap, it is necessary to equip the corresponding four-blade grinding machine to repair the thread in the aluminum spot welding production. The grinding frequency is about 40 ~ 50 times that of the ordinary carbon steel spot welding.
3) application of German aluminum Spot welding -- Delta Spot (electrode belt type aluminum Spot welding)
Austrian Fronius Delta Spot Spot electrode belt aluminum Spot welding process is to add a new electrode belt between the electrode and the workpiece, as shown in figure 3. During spot welding, the electrode is pressed against the electrode belt to contact the workpiece for welding. After each spot welding, the electrode belt will automatically move to the next position, so that the surface of the electrode is always clean, which solves the problem that aluminum spot welding is easy to bond the material from the base material, and ensures that each welding spot has a high quality welding condition. In addition, the introduction of the electrode belt increases the resistance, thus increasing the heat input to the broken aluminum alloy surface oxidation film, to ensure the quality of welding.
Different electrode strips can be selected for spot welding of different materials. Copper strip or nickel-plated steel strip can be used for spot welding of aluminum alloy. Delta Spot equipment can also realize steel and aluminum welding, aluminum and magnesium die casting welding, and has been applied to German high-end vehicle manufacturers, such as BMW, audi, Mercedes.